Solar modules, also known as photovoltaic modules, are often simply referred to as solar panels or photovoltaic modules. A solar module is a product made by connecting multiple individual solar cells in series and parallel as needed, and then encapsulating them using specialized materials and manufacturing processes.
Photovoltaic modules are the core and most important component of a solar power system. Their function is to convert solar energy into electrical energy, which is then stored in batteries or used to power loads. So, do you know what factors affect the output of photovoltaic modules? Today, let's take a look together.
1. Hot spot effect
In a series circuit, a shaded solar cell module will act as a load, consuming the energy generated by other illuminated solar cell modules. The shaded solar cell module will then generate heat, which is known as the hot spot effect.
This effect can severely damage solar cells. Some of the energy produced by sunlit solar cells can be consumed by shaded cells. And the cause of the hot spot effect could be as simple as a bird dropping.
To prevent solar cells from being damaged by hot spot effects, it is best to connect a bypass diode in parallel between the positive and negative terminals of the solar cell module to prevent the energy generated by the illuminated module from being consumed by the shaded module. When the hot spot effect is severe, the bypass diode may break down, causing the module to burn out.
2. PID effect
Potential-induced degradation (PID) occurs when a battery module is subjected to high voltage for an extended period, causing leakage current between the glass and encapsulation materials. This results in a large amount of charge accumulating on the cell surface, deteriorating the passivation effect and causing the module performance to fall below design standards. Severe PID can cause a single module to experience a power degradation of over 50%, thus affecting the power output of the entire string. PID is most likely to occur in coastal areas with high temperature, high humidity, and high salinity.
3. Microcracks in the battery cells
Microcracks are defects in solar cells. Due to the inherent characteristics of their crystal structure, crystalline silicon solar cells are highly susceptible to cracking. The manufacturing process for crystalline silicon modules is lengthy, and many stages can potentially cause microcracks in the cells (according to Professor Yang Hong of Xi'an Jiaotong University, there are approximately 200 possible causes in the cell production stage alone). The fundamental cause of microcracks can be summarized as the generation of mechanical or thermal stress on the silicon wafer.
In recent years, in order to reduce costs, crystalline silicon module manufacturers have been developing crystalline silicon solar cells that are getting thinner and thinner, thereby reducing the cells' ability to prevent mechanical damage.
In 2011, the German ISFH published their research results: based on the shape of microcracks in solar cells, they can be divided into five categories: dendritic cracks, mixed cracks, oblique cracks, cracks parallel to the main grid lines, cracks perpendicular to the grid lines, and cracks that run through the entire solar cell.
Different types of microcracks have different impacts on cell performance. Microcracks parallel to the main grid lines (Type 4) have the greatest impact on cell performance. Research shows that 50% of cell failures originate from microcracks parallel to the main grid lines. The efficiency loss from 45° inclined cracks (Type 3) is one-quarter that of cracks parallel to the main grid lines. Cracks perpendicular to the main grid lines (Type 5) have almost no impact on the fine grid lines, therefore the area causing cell failure is almost zero.
Research results show that when the failure area of a single cell in a module is within 8%, it has little impact on the module's power output, and 2/3 of the diagonal stripes in the module have no effect on the module's power stability.
